Why does an onboard amp in an active speaker pair better than separate amplification ? Are the drivers different than a passive speaker? Are the crossovers different than in a passive speaker? It seems the only thing active does is eliminate the need for an external amp.
An example would be the speaker designer could match the appropriate amp to the appropriate speaker driver to achieve their design goals optimally. Also, the designer can place the "crossover" at the point in the audio chain, again, to achieve their goals.
An extreme mismatch example would be for an active two way where the amp driving the top end was a class d plate amp and the low frequency driver driven by a class A 10 watt amp.